In view of the desire to conserve energy, it is important to consider all factors that could lead to improved efficiency of illumination, whether sunlight or electricity is used. In particular, some of the new high-efficiency illuminants such as mercury vapor or high-pressure sodium lamps, because of their very high luminosity, will require efficient light diffusers to reduce their specific brightness to a physiologically tolerable level.
An important property of a light diffuser is its ratio of forward-to-backward transmission, since light that is scattered backward into a light fixture, of necessity, will be partially absorbed. Certain rear projection screens have been optimized for this effect. Opal glass, which can be formed into a wide variety of luminary shapes, is the preferred solution in less critical applications, despite the fact that it often scatters more light backward than forward.
There exists a novelty device for producing interacting patterns of light reflection known commercially as a Kalliroscope (TM). This device uses myriads of organic crystals of guanine suspended in perchlorethylene to provide small platelets of high refractive index in a fluid of substantially equal density but lower refractive index. The alignment of the crystals is controlled by shear force induced by fluid flow of the perchlorethylene or by the application of an electric field to the fluid.
This interesting but relatively commercially useless novelty device caused the applicant to consider whether similiar principles could be utilized in apparatus which would be commercially useful as in a light diffuser. The Kalliroscope (TM) device was not suited for this application since it requires fluid motion to prevent settling of the platelets and a continuously applied electric field to produce the light transmission effect.
It is therefore the object of this invention to provide an improved light diffuser.
It is a still further object of this invention to provide a near-ideal light diffuser having the desirable properties of good diffusion of light, very high forward transmission with an inherently low light loss, and close-to-radial symmetry in the exiting light beam.
It is a feature of this invention that a practical and useful diffuser satisfying those objects is obtained by the permanent suspension of oriented platelets in a transparent material.